The present invention relates generally to welding and, more particularly, relates to an improved method and apparatus for producing uniform welding.
Laser welding is commonly used to join plastic or resinous parts, such as automobile thermoplastic parts, at a welding zone. An example of such use of lasers can be found in U.S. Pat. No. 4,636,609, which is expressly incorporated herein by reference.
As is well known, lasers provide a focused beam of electromagnetic radiation at a specified frequency (i.e., coherent monochromatic radiation). There are a number of types of lasers available; however, infrared lasers or non-coherent sources provide a relatively economical source of radiative energy for use in heating a welding zone. One particular example of infrared welding is known as Through-Transmission Infrared Welding (TTIR). TTIR welding employs an infrared laser capable of producing infrared radiation that is directed by fiber optics, waveguides, or light guides through a first plastic part and into a second plastic part. This first plastic part is often referred to as the transmissive piece, since it generally permits the laser beam from the laser to pass therethrough. However, the second plastic part is often referred to as absorptive piece, since this piece generally absorbs the radiative energy of the laser beam to produce heat in the welding zone. This heat in the welding zone causes the transmissive piece and the absorptive piece to be melted and thus welded together. However, the heat produced by conventional laser systems often fail to provide a consistent, reliable, and esthetically pleasing weld, which can lead to excessive waste and/or increased production costs.
Radiative energy produced by the infrared laser can be delivered to the targeted weld zone through a number of transmission devicesxe2x80x94such as a single optical fiber, a fiber optic bundle, a waveguide, a light guide, or the likexe2x80x94or simply by directing a laser beam at the targeted weld zone. In the case of a fiber optic bundle, the bundle may be arranged to produce either a single point source laser beam, often used for spot welding, or a generally linearly distributed laser beam, often used for a linear weld. Each of these arrangements and transmission devices suffer from a number of disadvantages inherent in their designs.
By way of example, a single optical fiber typically produces an output beam having a generally-Gaussian laser intensityxe2x80x94the center of the targeted weld zone receives an increased concentration of radiative energy relative to the outer edges of the weld zone. This increased concentration of radiative energy near the center of the weld zone often causes the center of the weld zone to become overheated, resulting in disadvantageous xe2x80x9cbubblingxe2x80x9d and/or out-gassing in the center area of the weld zone.
However, this overheating and the resultant xe2x80x9cbubblingxe2x80x9d and/or outgassing in the center area of the weld zone is not overcome simply by using a fiber optic bundle. Although it is known that a fiber optic bundle causes the generally-Gaussian or parabolic laser intensity output from a single optic fiber to be substantially normalized to produce an overall, generally uniform, laser intensity output, the center area of the weld zone is still often overheated. In the art, this overall, generally uniform, laser intensity output from a fiber optic bundle is known as a xe2x80x9ctop hatxe2x80x9d distribution, which is a relatively accurate representation in near-field applications.
However, what is not readily appreciated in the art today is that although a generally-uniform laser intensity output can be achieved using a fiber optic bundle, such uniform intensity beams do not necessarily reduce the overheating, xe2x80x9cbubblingxe2x80x9d, and/or out-gassing in the center area of the weld zone. Due to heat transfer principles, even with a uniform intensity beam, heat will build up faster in the center of the weld zone than along the edges of the weld zone.
Accordingly, there exists a need in the relevant art to provide an apparatus capable of producing an evenly distributed temperature profile throughout a target zone in order to produce a consistent weld joint. Furthermore, there exists a need in the relevant art to provide an apparatus capable of minimizing out-gassing or bubbling of a weld joint. Still further, there exists a need in the relevant art to provide an apparatus capable of redistributing radiative energy to the edge of a targeted weld zone to produce a more uniform temperature distribution. Additionally, there exists a need in the relevant art to provide an apparatus and method of using the same that is capable of overcoming the disadvantages of the prior art.
According to the principles of the present invention, a laser welding lens assembly for welding a first article to a second article at a weld zone is provided having an advantageous construction. The laser welding lens assembly includes a laser source outputting a laser beam. An optical fiber is operably coupled to the laser source to receive and transmit the laser beam. A lens is then positioned to receive the laser beam from the optical fiber. The lens includes a contoured face that is shaped to refract the laser beam to produce a generally uniform temperature profile across the weld zone.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.